Grants a 50% chance to avoid combat damage cast from spells, spell-like abilities, scrolls, or wands. If the resistance check succeeds, no damage is dealt. Combat Magic Resistance does not stack with anything else–either the magic works or it doesn’t. That said, if the Combat Magic Resistance check fails and the spell works, any other damage-mitigating effects the wearer may have would still apply.
It does not protect against spells which do not physically damage such as sleep,